The present invention relates to an image forming apparatus, such as a copier, a printer, etc.
Conventionally, an image forming apparatus employing the electro-photographic method, such as a copier, a printer, etc., is provided with a photoreceptor member serving as a image bearing member, a charging device, a scanning unit, a developing roller, which are sequentially disposed around the photoreceptor member, and a transferring roller serving as a transferring member.
In the image forming apparatus mentioned in the above, a surface of the photoreceptor member is uniformly charged by the charging device, and then, an electrostatic latent image is formed on the charged surface of the photoreceptor member by scanning a laser beam modulated on the basis of the image data and emitted from the scanning unit onto it. Then, the developing roller develops electrostatic latent image with toner to form a toner-image on the surface of the photoreceptor member. Successively, the toner image formed on the surface of the photoreceptor member is transferred onto a paper sheet serving as a recording medium by employing the transferring roller. Through the abovementioned process, the image can be formed on the paper sheet.
Further, there has been well known a color image forming apparatus, or the like, which is provided with a plurality of developing rollers each of which corresponds to each of unicolor images (primary colors) and an intermediate transfer member, serving as another image bearing member, for overlapping the unicolor images respectively formed on the photoreceptor member with each other on it, so as to form a full color toner image by sequentially overlapping the unicolor images one by one with each other. Then, the color image forming apparatus forms a full color image on the paper sheet by transferring the full color toner image on to the paper sheet by employing the transferring roller serving as a transferring member.
Conventionally, such the image forming apparatus mentioned in the above has formed the image on the paper sheet with margin spaces located around a peripheral area of the paper sheet. However, recently, there has been getting proliferated in the market such a print-outputting method, called as a marginless print, that extends the image forming area up to at least one of the margin spaces.
For instance, there has been well known a document processing technology, called as an index print, for automatically adding index characters to the left edge portion (or the right edge portion). Further, in recent years, there has been getting also proliferated in the market such a printing method, called as a whole marginless print, that extends the image forming area up to at all of the margin spaces without having any margin space, when printing a pattern image, a photographic image, etc.
Incidentally, when a positional deviation, caused by the erroneous conveyance timing shift, etc., is generated between the toner image formed on the image bearing member and the paper sheet, the position of the image formed on the paper sheet is different from that of the original image read from the document. In almost cases, amounts of the erroneous conveyance timing shift are not constant, but differ from each other depending on the differences between sizes and kinds of the paper sheets or kinds of containers accommodating the paper sheets.
Accordingly, when conducting the marginless print, a positional deviation generated between the toner image and the paper sheet causes a defect of the image transferred onto the paper sheet, resulting in a formation of a very awkward image. In addition, the defect of the image is also caused by the size variation of the paper sheets.
To overcome the abovementioned drawbacks, considering the positional deviation caused by the erroneous conveyance timing shift and the size variation of the paper sheets, there has been conducted such an operation that a large-sized toner image, having a sufficient allowance, is formed on the image bearing member, so as to form a good image over the paper sheet without forming any defect, even if the erroneous conveyance timing shift of the paper sheet occurs.
When the marginless print is conducted over the edge portion of the paper sheet by employing the abovementioned operation, there has raised a problem that the surface of the transferring roller is contaminated by toner, and such the contaminated transferring roller causes the toner scattering inside the printer apparatus. Specifically, when the toner image, residing on the image bearing member and extended from the recording medium, directly contact the transferring roller, the toner is firmly absorbed and attached onto the transferring roller due to a combination of the contacting pressure of the transferring roller and the transferring electric field. It is quite difficult to clean the toner firmly absorbed and attached onto the transferring roller, and, especially for the high density image, even if the mechanical cleaning device, such as blade, etc., is employed for cleaning, sometimes, the reverse surface of the paper sheet would be contaminated, due to an occurrence of the toner passing-through phenomenon.
Further, when the polymerized toner, whose particle diameter is minimized and whose circularity is high, are employed in order to cope with the recent demands for high quality imaging, or when an amount of attached toner is relatively high as in the full-color image forming apparatus, it has tended to become more difficult than ever to secure the cleaning efficiency.
Still further, when the residual toner, which are not transferred onto the paper sheet, increase more than ever, there has raised a big problem that the toner scattering phenomenon causes the contamination inside the apparatus.
To solve the abovementioned problems, the several countermeasures have been proposed in this field.
For instance, to solve the problem of the contamination on the transferring roller when the index print operation is conducted at the edge portion of the paper sheet, Patent Document 1 sets forth a solution in which an interval between paper sheets is set at a value wider than that of a normal case, and the transferring process and the cleaning sequence are alternately conducted.
Further, Patent Document 2 sets forth a measure for preventing the contamination of the transferring roller and the contamination of the reverse surface of the paper sheet by conducting the transferring operation with a gap between the photoreceptor member and the transferring roller.
Still further, Patent Document 3 sets forth a method for making it possible to prevent an occurrence of the contamination so as to form a good full image by conducting the image forming operation in a state that a guiding paper sheet, which is larger than the paper sheet, is extended from the four edges of the paper sheet.
Yet further, Patent Document 4 sets forth a measure for cleaning the transferring roller by employing the cleaning blade.
[Patent Document 1]                Tokkai 2004-309696 (Japanese Non-Examined Patent Publication)        
[Patent Document 2]                Tokkaihei 5-158361 (Japanese Non-Examined Patent Publication)        
[Patent Document 3]                Tokkai 2005-17570 (Japanese Non-Examined Patent Publication)        
[Patent Document 4]                Tokkaihei 6-118805 (Japanese Non-Examined Patent Publication)        
However, the conventional technologies mentioned in the above still include various kinds of drawbacks to be solved.
According to the technology set forth in Patent Document 1, when forming a high density image so as to output it onto the recording medium, repetitions of plural cleaning operations should be necessary for achieving the sufficient cleaning effect, resulting in an extreme deterioration of the print productivity.
According to the technology set forth in Patent Document 2, it is impossible to sufficiently cope with the thickness changes between the recording mediums. Further, since a discharging phenomenon is liable to occur due to the loose contacting state between the photoreceptor member and the transferring roller, sometimes, it is impossible to obtain a good image. In addition, since the conveyance efficiency of the recording medium is lowered, the problem, such as the misalignment of transferred images, etc., is liable to occur.
According to the technology set forth in Patent Document 3, there have been arisen not only the problem of wasting the guide papers, but also various kinds of other problems in regard to the contacting property between the paper sheet and the guide paper. When those are close-contacted with each other by the electrostatic action, those would possibly shift or separate form each other in a mid course of the conveying operation.
According to the technology set forth in Patent Document 4, the cleaning mechanism has become complicated, and further, sometimes, a toner filming phenomenon has occurred on the transferring roller. Further, when the toner, such as the polymerized toner, etc., whose circularity is high, are employed, sometimes, a problem with respect to the cleaning efficiency has been arisen.